This invention relates to the field of antennas, and more particularly, to antenna structures for covering a diversity of frequency bands.
A large number of different radio frequency systems have come into use for communication, navigation, electronic warfare and radar systems. State-of-the-art automotive and aerospace-borne vehicles which utilize such radio frequency systems could have more than a dozen separate antennas to cover a diversity of frequency bands. However, many mobile platforms have limited space for multiple antennas operating in widely separated frequency bands.
Alternatively, a number of wide bandwidth antenna elements have been developed for electronic warfare and signal intelligence systems. Current state-of-the-art antennas include flared notch elements, each with about an octave of bandwidth (2:1). Other antenna elements such as spirals, log periodic elements, biconical dipoles and conical monopoles all have a bandwidth limit of about 2:1 and they tend to have relatively large physical dimensions and, as such, are not well-suited for mobile platform vehicular use.
One solution to this multi-antenna, multi-aperture problem now faced by land, sea, air and space-borne vehicles has been multi-function, multi-frequency, phased array antenna apertures with electronic beam forming and scanning/tracking. However, today broadband antenna elements and phased array antennas are limited by the bandwidth and dimensions of the antenna-feed elements to a maximum frequency ratio of about one octave (2:1). Broad bandwidth phased array antennas composed of broadband feed elements must address several conflicting design parameters:
1) low side lobes require that the phase centers of the feed antennas be closely spaced one half wavelength apart at the highest frequency of operation;
2) feed antennas have dimensions approaching one half wavelength at the lowest operating frequency;
3) large numbers of broadband amplifiers must be connected to every feed antenna in a 2:1 bandwidth array; and
4) a second set of crossed linear antenna elements and associated electronics often are required if the array is to transmit and receive signals in orthogonal linear polarization and in both circular polarizations.
Therefore, there exists a need for an effective antenna structure which can cover a diversity of frequency bands, a diversity of polarizations, and can be useful in phased array antenna systems. The present invention provides a unique solution to meet such needs.
In accordance with the present invention, an inventive three dimensional, ultra-broad bandwidth, multi-aperture, dielectric antenna is provided which combines features of tapered dielectric rod antennas and coaxial dielectric waveguide transmission lines. The coaxial dielectric rod antenna (CDRA) in accordance with the present invention has multi-frequency collinear apertures which can be optimized for use as individual multi-band antennas or as feed elements in broad bandwidth active aperture phased array antennas. In essence, the CDRA in accordance with the present invention combines into a single structure many separate antennas which cover a diversity of frequency bands.
A first embodiment of the invention includes a first dielectric antenna rod having a first dielectric constant. The first dielectric antenna rod is coupled to a first frequency transmission source for propagating first frequency band radiation from the first dielectric antenna rod into a medium having a medium dielectric constant. A second dielectric antenna rod is provided having a second dielectric constant. The second dielectric antenna rod is coupled to a second frequency transmission source for propagating second frequency band radiation from the second dielectric antenna rod into the medium. The first dielectric antenna rod is coaxially mounted within the second dielectric antenna rod. The first dielectric constant is greater than the second dielectric constant. The second dielectric constant is greater than the medium dielectric constant.
In accordance with the first embodiment, the second dielectric antenna rod can include an axial cylindrical cavity along the length of the second dielectric antenna rod. The axial cylindrical cavity can be filled with a dielectric powder having the first dielectric constant. The dielectric powder can be secured within the axial cylindrical cavity by end plugs having the first dielectric constant and be located at respective proximal and distal ends of the second dielectric antenna rod. Further, the first frequency transmission source can be axially coupled to the first dielectric antenna rod while the second frequency transmission source can be coupled to the second dielectric antenna by a transmission line axially offset from the second dielectric antenna rod. The second dielectric antenna rod can be made of a thermoplastic resin. The dielectric powder can be barium tetratitanate or nickel-aluminum titanate.
Another embodiment of the present invention includes a first dielectric antenna rod having a first dielectric constant. The first dielectric antenna rod is coupled to a first frequency transmission source for propagating first frequency band radiation from the first dielectric antenna rod into a medium having a medium dielectric constant. A second dielectric antenna rod is provided having a second dielectric constant. The second dielectric antenna rod is coupled to a second frequency transmission source for propagating second frequency band radiation from the second dielectric antenna rod into the medium. The first dielectric antenna rod is coaxially mounted within the second dielectric antenna rod. A third dielectric antenna rod having a third dielectric constant is also provided. The third dielectric antenna rod is coupled to a third frequency transmission source for propagating third frequency band radiation from the third dielectric antenna rod into the medium. The second dielectric antenna rod is coaxially mounted within the third dielectric antenna rod. The first dielectric constant is greater than the second dielectric constant. The second dielectric constant is greater than the third dielectric constant. The third dielectric constant is greater than the medium dielectric constant.